Cyber Week5 - MLS,CovertChannels,PowerAttacks

What is the primary characteristic of Discretionary Access Control (DAC)

The user determines who is given access to objects they own

What is a major vulnerability of DAC systems regarding program behavior

DAC does not provide protection against Trojan Horses

How does Mandatory Access Control (MAC) differ from DAC

The system assigns security attributes to subjects and objects which cannot be changed on request

What is MLS and which kind of Access Control is it likely to use?

Multi-Layer Security is a security policy based on classifications, commonly used in highly assured networks e.g. Government. Uses Mandatory Access Control.

What is classification in the context of MLS

A hierarchical set of markings indicating levels of sensitivity like Top Secret or Secret

What does the ‘dominates’ relation signify

It means a classification is “at least as sensitive” as another

Name the three mathematical properties of the dominates relation

Reflexive (each classification dominates itself)

Asymmetric (different classifications cannot both dominate the other)

Transitive (If A > B and B > C, then A > C)

In MLS what is classification and clearance

Objects are assigned a classification indicating the sensitivity of their data.

Subjects are assigned a clearance - a classification which indicates the most sensitive data they can read/write.

State the Bell-La Padula No Read-Up Rule

A subject may only read an object if the subject clearance dominates the object classification

Why is the No Read-Up rule not enough to provide security on its own?

A user may read contents of a secret file and copy them to an Unclassified file

State the Bell-La Padula No Write-Down Rule (star-property)

A subject may only write to an object if the object classification dominates the subject clearance

What is the purpose of a current clearance

To allow a subject to operate at a lower sensitivity level than its maximum clearance to avoid overly restrictive write-rules

What is a covert channel

An unusual means of communication that allows information to leak in violation of mandatory security policy

Define a covert storage channel

A channel where the values returned to a receiver by system operations are modulated to convey data

Define a covert timing channel

A channel where the time at which events are perceived by a receiver is modulated to convey data

How can the existence of a file be used as a covert channel

A high-level subject creates or deletes a file and a low-level subject tries to create the same file to see if it already exists

How can object attributes like Time Last Read be used covertly

A high-level subject reads a file which updates its metadata and a low-level subject monitors that metadata for changes

What is the security risk of downgrading an object

It allows a user to reclassify sensitive information (e.g. Top Secret) to a lower level (e.g. Unclassified)

Explain a timing channel using a disk head

A sender moves the disk head to a specific radius and the receiver measures the time taken for its own disk access to infer the sender bit

What is a system clock in the context of covert channels

A means for a receiver to measure the passage of relative time to interpret timing signals

What is the Goguen and Meseguer non-interference model

The principle that actions by high-level subjects should not be visible to or affect lower-level subjects

List two ways information can be covertly channeled in distributed systems

By modulating message lengths or the timing of messages

Why might overwriting a file with zeros not be enough for security

Finer physical analysis like scanning force microscopy may reveal traces of the previous data history

How can signal amplitude be used for a covert channel

By using small voltage excesses over the reference values (e.g. 0.1V above 5V) to signal hidden bits

What does it mean to slug a covert channel

To increase the time taken to complete actions to reduce the channel bandwidth and make it less useful

What are caveats and codewords in MLS

Additional markings used to restrict information to specific groups or reflect a need to know

What mathematical structure is formed by compound security classes

A lattice

In a lattice what is the Least Upper Bound (LUB)

A unique security class that dominates two given classes

What is Biba's model used for

Maintaining system integrity by preventing low-integrity subjects from writing to high-integrity data

What is the dual of secrecy in the Biba model

Integrity

What is the core premise of a Power Attack

Monitoring power consumption of a hardware implementation can reveal secret key information

Define Simple Power Analysis (SPA)

An attack that involves directly observing power traces to identify executed instructions or key bits

Define Differential Power Analysis (DPA)

An attack that uses statistical correlations across many executions to extract secret keys

How can SPA reveal the DES algorithm's execution

The 16 rounds of DES encryption show up as visible power consumption profiles over time

How can SPA reveal a secret key via conditional branches

If an algorithm executes different instructions based on a 0 or 1 key bit the power profile will change

Name one way to defend against SPA

Avoid conditional branching or generate noise to mask the power profile

What is the first step in a DPA attack

Guessing a portion of the sub-key bits (e.g. for a DES S-box)

What is a predictor in a DPA attack

A function used to predict a specific bit value in the calculation based on a key guess and ciphertext

How does the DPA predictor act as a partitioner

It splits power traces into two groups based on whether the predicted bit is 0 or 1

In DPA what happens to the power average if a key guess is wrong

The difference between the two partitioned groups will be very small or near zero

In DPA what happens if a key guess is correct

A correlation spike appears because the two groups have different power consumption averages

Why are power attacks considered side-channel attacks

Because they exploit physical information leaked by the hardware rather than flaws in the math of the algorithm